Fluoropolymers are traditionally used for applications requiring special properties, such as low surface energy, high resistance to chemical attack, aging resistance, and electrochemical stability. However, these advantageous properties also make fluoropolymers difficult to work with and limits their applications. For example, the lack of functional groups on the fluoropolymers makes them difficult: to adhere to substrates, to facilitate cross-linking, to provide sites for subsequent chemical modification, to be wetted by water, and to add hydrophilic characteristics. There is a need for fluorinated polymers having modified properties, such as functional groups, which can augment their properties. Fluoropolymers have been post reaction grafted, such as with maleic anhydride to add functionality (U.S. Pat. No. 7,241,817 and U.S. Pat. No. 8,182,912).
However it is difficult to add functional monomer units directly into the polymerizing polymer backbone, especially in a random manner, due to the aggressive nature of the fluorine-containing free radicals.
US 2008-0249201 describes sequential polymerization of vinylidene difluoride (VDF) followed by polymerization of vinyl acetate (VAc) polymerized within the pores of the PVDF particles. This assures intimate blending, but does not form a random copolymer.
U.S. Pat. No. 5,415,958, discloses copolymerization of vinylidene fluoride with an unsaturated dibasic acid monoester polar monomer; to introduce carbonyl groups to the backbone of PVDF in order to improve its adhesion to different substrates.
An article by V. Panchalingam and J. R. Reynolds describes the copolymerization of VAc with VDF. (J. Polm. Sci Part C 27 201 (1989). The resultant copolymers did not have uniform distribution of VAc. Their characterization proved that one phase was rich in VAc and the other phase was reach in VDF.
It has now been found that random copolymers of fluoropolymers, and especially vinylidene fluoride, and be copolymerized with vinyl esters, so that a minimum of 40% of the vinyl ester monomer units exist as single units within the polymer backbone.